The present invention relates to a seeking operation control apparatus in an optical disc reader. More specifically, it relates to a seeking operation control apparatus in an optical disc reader which seeks a desired track on an optical disc by a rough access operation followed by a finishing access operation.
The compact disc (hereinafter referred to as CD), a type of optical disc, has become very popular and has superseded the LP record in the field of audio reproduction systems. In conjunction with the more widespread use of CDs, the CD as a read-only memory (CD-ROM) has come into standardization. The CD-ROM is a 12 cm-diameter CD for storing data and programs, from which a computer can read the information stored.
Comprising a spiral line on the CD-ROM are the tracks which store information, including information as to the tracks themselves. Seeking a desired track, an optical disc reader first performs a rough access operation followed by a finishing access operation. During the rough access operation, the optical disc reader calculates the number of tracks to be jumped and drives an optical pickup to jump the tracks to approximately the desired position, in a lower accuracy phase. Then, the optical disc reader reads track information from the track onto which the optical pickup has been located, and calculates the number of tracks still to be jumped. If the finishing access operation is permissible, i.e., provided that the optical pickup is located within an area which includes the precise position desired, then under control by the optical disc reader, the optical pickup jumps tracks accurately, whereupon the optical pickup reads current track information again. The optical disc reader locates the optical pickup precisely to the desired track by repeating the above seeking operations.
The seeking speed of the optical disc reader utilizing the above operations is superior to that of magnetic tape readers, yet it is inferior to that of hard disc readers. Therefore, faster search operation in optical disc readers has been an object of research.
A conventional optical disc reader requires a considerable period of time in order to position the optical pickup onto the desired track, since it reads track information after every track jump, which amounts to several times in the finishing access operation. The track-information reading operation costs a certain length of time, resulting in prolonged seeking time, due to the fact that many processes (correction for example) are involved in the track-information reading operation.
Another optical disc reader performs various types of jump operations in which one-track jumps, three track jumps, five-track jumps, etc. are involved, and selects the proper category of jump depending upon the number of calculated tracks to be jumped. However, due to the necessity of selecting a jump type, this optical disc reader requires complex control, which in turn must be implemented by complex software.